Transferring GBP to Swissquote

Has anyone managed to successfully transfer money to Swissquote’s GBP account without loosing ~£20 along the way? I have tried doing it from Interactive Brokers (CapTrader actually) and incurred the loss due to some intermediary bank. I am tempting to try routing it via my Transferwise account, but I expect it to be the same problem as it will be transferring from UK to CH again…